Special chars '+', '-'. '""  modify the default search criteria in the search as you type feature.

https://docs.telerik.com/devtools/wpf/controls/radgridview/features/search-as-you-type#modifying-the-searching-criteria

Add option to disable this behavior. It would be useful in scenarios with strings starting with + or -.
Also option should be available for setting in MultiColumnComboBox.